Chaeles e



(No Model.)

o. E. SGRIBNBR zzz-G. D. CLARKE.

. CARBON 0F TELEPHONE TRANSMITTERS'.

` Patented Jan. 10.1882..

Idlll UNITED STATESv PATENT OFFICE.

CHARLES E. SCRIBNER AND GEORGE D. CLARKE, OF CHICAGO, ILLINOIS, ASSIGNORS TO THE WESTERN ELECTRIC MANUFACTURING COMPANY,

OF SAME PLACE.

v CARBON OF TVELEPHONE-TRANSMITTERS.

SPECIFICATION forming part of Letters Patent No. 252,296, datedV January 10, 18.82,

Application tiled October 18, 1880. (No model.) -Putented inuEngland November 29, 1879. f

To all whom it may concern: Be it known that We,CHARLEs E. SCRLB- NEE and GEORGE D. CLARKE, citizens of the United States, and residents of Chicago, in the county of Cook and State of Illinois, have invented certain new and useful Improvements in the Carbons of TelephoneTransmitters, of which the following is a full,`clear, concise, and exact description, reference being,` had to the ro accompanying drawing, forming a part of this specification.

Our invention consists in providing a roughened surface which rests in contact with the soft carbon button. The soft carbon is placed in the rubber cup, with its lower surface resting upon a metallic surface, usually of platinum. Prior to our invention the upper surface of the carbon was placed in contact with the lower surface of a metallic disk. y.

In carbon-transmitters the best resultsare obtained when this upper surface ot' the sot't carbon is slightly roughened. The roughened surface which produces the best results has been compared to a surface of velvet, which 25 may be formed by light strokes ot' a fine brush.

` When used in combination with a metallic disk placed above it this velvety or roughened surface is soon destroyed, and becomes smooth and covered with a' thin glossy scale.

IVe have discovered that a disk of hard carbon substituted for the metallic disk will keep the surface ofthe soft carbon in the proper condition. It is not absolutely necessary to use the brush, as the surface of hard carbon, when placed in contact with the soft carbon,soon

produces a surface ot' the required properties.

The surface of hard carbon should be made perfectly true,in orderthat its every pointmay 11nd contact with the upper s-urf'ace of the soft- 4o carbon button.

We true or level the hard carbon by friction Vpreferably against emery-paper. We electroplate the upper surface ot' thehard carbon pret'- erably with copper. y

in batteries.

In the drawing, the figure is a section ofthe interior parts ot' a carbon-telephone embodying our improvements.

The diaphragm ais insulated, by insulating substance b', from thepointb, whichresls upon the copper-surface c ot' the hard carbon c. 5o

We find it most convenient to insulate the hemisphere b by japanuing the diaphragm in the. usual manner. The soi't-carbon button d is placed' Within the rubber cupfin the usual manner, and the circuit passes in the usual manner from the frame K and bed-piece L through the carbons., and, by conductor g, to a binding-post provided in the usual manner upon the frame of the telephone.

The hard carbon referred to posseses the 6o` characteristics or properties ofthe carbon used The soft carbon may be made ot' lamp-black, and the buttons ot'sol't carbon may be formed in a press, enough pressure being applied to cause the buttons to retain their form When handled with care.

We claim- 1. In a carbon-telephone, the combination of a piece of hard carbon with the but-ton of sott carbon, the hard carbon being provided with 7o a true surface, Which is in contact wir h the soft carbon, the hard-carbon and sott-carbon buttons thus combined forming the contact-elec` ,trodes or medium ot' variable resistance, as and for the purpose set forth. l

2. In a telephone-transmitter, the conibination of a piece of hard carbon, with its upper surface coated with metal, and the button of sott carbon, and the diaphragm, the piece 'ot' hard carbon and the button ol' soft carbon hav- 8o ing,` surfaces in Contact and forming the contact-electrodes, substantially as and for the purpose specied.

CHARLES E. SCRIBNER. GEORGE D. CLARKE.

Witnesses: i

GEORGE P. BARTON, WALLACE L. DE WOLF. 

